1. Field of the Invention
This invention relates to a method for producing a bonded wafer, and more particularly to a method for producing a bonded wafer in which an oxygen ion implanted layer is provided on a wafer for active layer as an etching stop layer.
2. Description of the Related Art
The bonded wafer normally means a bonded SOI wafer. As a production method thereof are mentioned, for instance, a method wherein an oxidized wafer for active layer is bonded to a wafer for support substrate and thereafter a surface of the wafer for active layer is thinned to a given thickness by grinding and polishing as disclosed in a literature, “Science of Silicon”, edited by USC Semiconductor Substrate Technology Workshop, published by REALIZE INC. on Jun. 28, 1996, pp 459-462, and an ion implantation-isolation method or a so-called smart cut (Smart Cut (registered trademark)) method comprising a step of forming an ion implanted layer by implanting, ions of a light element such as hydrogen, helium or the like into a wafer for active layer at a given depth position, a step of bonding the wafer for active layer to a wafer for support substrate through an insulating film, a step of exfoliating at the ion implanted layer and a step of thinning a portion of the active layer exposed at a state bonded to the wafer for support substrate by exfoliation to form an active layer of a given thickness as disclosed in WO 2005/074033.
In the above silicon wafer, it is assumed that it is important to make the thickness of the active layer thin and to enhance the uniformity thereof. To this end, the inventors have also disclosed the production technique of a bonded wafer satisfying the requirements for the thinning and the uniformity of the thickness of the active layer in WO 2005/074033.
In the technique disclosed in WO 2005/074033, however, when oxygen ions introduced in the oxygen ion implantation (oxygen ion implanted layer) do not form a complete oxide film and is existent at a discontinuous state, an etching solution-penetrates from a portion of the wafer not forming the oxide film to remove the active layer at a subsequent step (at a time of exposing the oxygen ion implanted layer), and hence the thickness uniformity of the active layer may be deteriorated and defects may be caused. Although the deterioration of the thickness uniformity and the occurrence of defects may be reduced at a next oxidation treatment step and at a step of removing an oxide film, it is particularly feared that the defects are further increased at a step of heat treatment.